This invention relates to a method and system for processing coating consolidation data of a moving web.
A system for depositing a coating on a web generally has a take up reel and a supply reel arranged to move the web along a path from the supply reel to the take up reel, but could also be an integral part of a complete paper making machine. A coating station that deposits a coating on the moving web is disposed along the path followed by one or more dryers that dry the coating before the web is taken up on the take up reel or passed on to the next part of the paper making machine.
In the production of pigment-coated paper or paperboard, the method and rate of drying of the coating significantly influences the print quality of the finished product, as noted by Voss, H., and Gxc3xa4rber, W. E., xe2x80x9cCorrelations Between Drying Conditions And Quality Of Coated Paperxe2x80x9d, 1975 TAPPI 58 (9) pages 99-103, Graab, H., xe2x80x9cDrying Of Coated Papersxe2x80x9d, translated by IPST from Wochenbl. Papierfabr. 111, No. 17: 645-646, 648-649 (Sep. 15, 1983). Improper drying during initial stages can cause binder migration that leads to its non-uniform concentration on the surface of the coating, or pore structure variations across the surface (Xiang, Y., Bousfield, D., Coleman, P., and Osgood, A., xe2x80x9cThe Cause of Backtrap Mottle: Chemical or Physical?xe2x80x9d, 1999). Such effects are thought to cause print mottle, which is the primary reason for poor print quality.
Gloss is the ratio of specularly reflected light to incident light. For optically smooth surfaces, gloss varies with refractive index and angle of incidence according to Fresnel""s law. Gloss is also a function of roughness and can be used to characterize surface roughness. When the roughness is of the same order of magnitude as the wavelength of light, (xe2x80x9cmicroscopicxe2x80x9d roughness), gloss varies exponentially with the ratio of roughness to the wavelength of light.
In recent years, much work has been done to model the coater drying and predict dryer settings that optimize final quality. Part of the modeling is a calculation of the gel point of the coating, i.e., the location of the web path at which binder immobilization has occurred. This calculation requires extensive man-hours to determine the specific values of each parameter to apply to the model for each grade on each coater. Parameters that are required for the modeling include coat weight, temperature, and moisture, among others.
Finnish Patent No. 71,020 describes a method for following the solidification process of pigment coatings on paper, especially for on-line operations. According to the method, the paper is illuminated and the intensity of the transmitted light, the brightness of the paper and/or the gloss of the paper are determined as a function of time elapsed from the moment of the application of the coating.
French Patent No. 2,667,940 describes a method to give a continuous measurement of the dynamic water retention in a coated web, particularly paper after a fluid coating application. A wave train in a known frequency spectrum is generated at a plane in relation to the moving web and at a different incidence angle from the standards to the plane defined by the web, at a gap of 0-2 m from the coating station. The receivers are on the same plane as the signals of the wave train reflected from the web. The values of the received signals are used to register the volume of the damp applied coating layer. Each measurement is repeated at an interval that is greater than the gap between the first measurement and the coating station, but less than 2-20 m from the coating station, to give values of the same level to show the changes over time to base the control for a constant web speed of travel. The mean rise in the change indicates the penetration speed of the fluid in the web and the sought-for dynamic retention of the fluid in the web.
U.S. Pat. No. 6,191,430 B1 describes a system having a measuring device that provides a comparison of the specular and diffused radiation reflected from a coating that can be used in ratio to locate the gel point of the coating and to monitor coating drying characteristics. The gel point data is compared to base line data. The system may also be used to monitor the drying process of the coatings in an off-line lab setting to obtain off-line data that may be used to help calibrate on-line gel point sensor systems.
U.S. Pat. No. 5,124,552 describes a measuring device that incorporates an infrared web moisture sensor and a web temperature measurement. It comprises a source of infrared radiation and infrared-detecting units, which measure the infrared beam at three separate wavelength regions. The first wavelength region is primarily sensitive to the moisture content of the web, the second wavelength region is less sensitive to the moisture content, and the third wavelength region provides an indication of the web temperature.
U.S. Pat. No. 4,957,770 describes a sensor and a method for determining the basis weight of coating material on a substrate is described. The determined basis weight is insensitive to changes in the amount of substrate material underlying the coating. Signals from the sensor may be used in the control of a coating mechanism to provide a coating having a uniform basis weight.
What is needed is a system and method that produces machine direction data along a moving web that is based on measurements of a large number of variables at enough locations to account for non-linearities.
There is also a need for a system and method that dynamically updates machine direction data derived from measurements taken at a plurality of locations along a moving web.
The system of the present invention processes signals that are sampled at essentially the same cross or lateral direction (CD) locations and at different machine direction (MD) locations along a moving web. The system includes a plurality of sensors disposed at the CD locations. Each sensor includes at least one unit for directing a beam of radiation on the web and at least one unit for receiving radiation returning from the web. A measurement processor processes the returned radiation to produce signal samples of measurements of two or more characteristics of the web for each of the MD locations. A computer performs the operations of:(a) combining the signal samples to produce at least one machine direction profile of a characteristic of the web; and combining the at least one machine direction profile with correction data to produce a corrected machine direction profile of said characteristic. The correction data is obtained from a quality control system and/or distributed control system and includes variables, such as dryer air temperature, web temperature, web moisture content, web basis weight, dryer air pressure, web speed, base paper, coating formulation, coating weight and infrared energy.
The method of the present invention processes signals sampled at different locations along a machine direction of a moving web. The signal samples are combined to produce at least one machine direction profile of a characteristic of the web. The machine direction profile is combined with correction data to produce a corrected machine direction profile of the characteristic.
According to an aspect of the invention, the signals sampled at each location represent one or more of the group consisting of: moisture content, gloss, color, clay content, latex content, CaCO3 content, smoothness and temperature.
According to another aspect of the invention, the corrected machine direction profile is presented to a user.
According to another aspect of the invention, the corrected machine direction profile is used to control a system that moves the web and/or performs operations on the web. The operations may include coating the web with a wet material and drying the coated web.
According to another aspect of the invention, the correction data include one or more from the group consisting of: dryer air temperature, web temperature, web moisture content, web basis weight, dryer air pressure, web speed, base paper, coating formulation, coating weight and infrared energy.
According to another aspect of the invention, the signals are sampled at a first rate and the corrected machine data is dynamically updated at a second rate, which is the same as or slower than the first rate.